The invention relates to a measuring device. The measuring device includes a cylindrical connection piece and a collar which engages around at least one section of the connection piece and is fastened at a measuring location. A restraining means fastens the connection piece in the collar. An annular seal is arranged in the collar and bears in a sealing manner against the connection piece. A thrust ring is releasably fastened in the collar and, in an end position, puts the seal under pressure in the axial direction.
Such measuring devices are commercially available. The cylindrical connection piece is fastened at a measuring location, for example in an opening on a tank or container. Examples are measuring probes, in particular capacitive filling level probes and vibration limit switches. In many applications, for example in chemistry or in the food industry, the containers are under pressure.
The connection piece is typically inserted into a tubular collar, which is screwed on at the measuring location, for example by means of a thread formed on it. The sealing of the interior space of the container with respect to the ambient takes place by the seal. This seal usually rests on a shoulder surface in the collar and the thrust ring has to be screwed into the collar. In the screwed-in state, the thrust ring is in an end position in which it presses with an annular end face against the seal. This restraining action between the shoulder surface and the annular surface makes the seal effective.
The restraining means usually comprises fixing screws which have to be screwed against the connection piece through through-bores which are arranged on the side facing away from the seal, penetrate the thrust ring and run perpendicularly with respect to the longitudinal axis of the latter.
An example of this prior art is represented in FIG. 1 and explained in more detail below.
One disadvantage of these measuring devices is that the fixing screws have the effect of a punctiform restraining action on the connection piece. The connection piece may be damaged, for example pressed in, by this localized loading. If the measuring device is used repeatedly, there is the risk of the damaged location being next to the seal and of the sealing quality being impaired.
When removing the measuring device, first of all the restraint of the connection piece in the collar has to be released and only then the restraint of the seal. After releasing the restraint, the connection piece is movable in the collar. It therefore goes without saying that the restraint may be released only when the pressure prevailing at the measuring location is equal to the ambient pressure. Otherwise, the measuring device could be forced out of the collar by a positive pressure prevailing at the measuring location, or be sucked into the container by a negative pressure prevailing at the measuring location. Under some circumstances, it is only with difficulty that the measuring device can be retrieved from the container.
A further disadvantage is that, when fitting on the measuring device, first of all the restraint of the seal takes place, and only then the fastening of the connection piece in the collar.
A further disadvantage is that, during mounting, two operations are required, one for restraining the seal and another for fastening the connection piece. This applies analogously for the demounting of the measuring device.